MAINTAINERS: erofs: Add Documentation/ABI/testing/sysfs-fs-erofs

Add this doc to the erofs maintainers entry.

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230209052013.34952-1-frank.li@vivo.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>